The present invention relates generally to a refrigeration system used in a frozen dessert system that includes a hopper heat exchanger and a cylinder heat exchanger that each contain a frozen dessert mix and have a respective expansion device, and a valve is positioned between each of the respective expansion devices and a heat rejecting heat exchanger to control a flow of refrigerant from the heat rejecting heat exchanger and into the hopper heat exchanger and the cylinder heat exchanger.
A refrigeration system is employed to cool a mix in a frozen dessert system. The frozen dessert system typically includes a hopper which stores the mix and a freezing cylinder that cools and mixes air into the mix prior to serving. The freezing cylinder is cooled by a refrigeration system. Refrigerant is compressed in a compressor to a high pressure and high enthalpy. The refrigerant then flows through a condenser where the refrigerant rejects heat and is cooled. The high pressure low enthalpy refrigerant is then expanded to a low pressure. After expansion, the refrigerant flows through the tubing encircling the freezing cylinder, accepting heat from and cooling the freezing cylinder, and therefore the mix. After cooling the freezing cylinder, the refrigerant is at a low pressure and high enthalpy and returns to the compressor for compression, completing the cycle.
The hopper is cooled by a separate glycol system that wraps around the hopper and the freezing cylinder. The glycol that flows around the freezing cylinder is cooled by the freezing cylinder. The cooled glycol then flows around the hopper to cool the mix in the hopper. To meet food safety standards, the mix in the hopper must be kept below 41xc2x0 F.
The mix is also pasteurized every night to kill any bacteria. The mix is heated for approximately 90 minutes to obtain a temperature of at least 150xc2x0 F. The mix is kept over 150xc2x0 F. for 30 minutes, and then cooled back to 41xc2x0 F. within 120 minutes. The mix is heated by heating the glycol with an electrical heater. As the heated glycol flows around the hopper and the freezing cylinder, the heat in the glycol is transferred to the freezing cylinder and the hopper, warming the mix.
A drawback to this system is that both the freezing cylinder and the hopper are coupled by the glycol system. During cooling, when the cooled glycol flows around and exchanges heat with the hopper, the glycol is heated by the hopper. When the glycol later flows around the freezing cylinder again, the heat in the glycol heats the freezing cylinder, melting the mix in the freezing cylinder.
Additionally, during heating, the glycol first flows around and heats the freezing cylinder. As the glycol rejects heat to the freezing cylinder, the glycol is cooled. When this glycol flows around the hopper, it is less effective in heating the hopper as the glycol has already been cooled by the freezing cylinder. Therefore, it takes longer to heat the hopper, resulting in a long pasteurization cycle which requires over three hours to complete. As the pasteurization cycle changes the flavor of the mix, a longer pasteurization cycle can affect the flavor of the frozen dessert.
Hot gas heating systems have been used in the prior art, but did not allow for individual control of the cooling of the hopper and the cylinder. Therefore, both the hopper and cylinder were cooled at the same time and could not be cooled separately. If only one of the hopper and the freezing cylinder required cooling, the other would have to be cooled as well. As the suction lines of the hopper and the freezing cylinder of the prior art are also not de-coupled, it is difficult to vary the pressure, and hence the temperature, of the refrigerant in the hopper and the freezing cylinder. To achieve the best dessert product quality, it is desirable to have the refrigerant cooling the mix in the hopper be at a different temperature and pressure than the refrigerant freezing the mix in the freezing cylinder. Another drawback of the prior art hot gas system is also that there is a low system capacity as an undersized compressor is employed to attain compressor reliability.
The hot gas heat treat system of the present invention includes a hopper which stores mix for making a frozen product. The mix flows from the hopper into a freezing cylinder for cooling and mixing with air. The refrigerant is compressed in a compressor and then cooled by a condenser and changes to a liquid. The refrigerant is then split into two paths, one flowing to the freezing cylinder and one flowing to the hopper. The refrigerant flowing to the freezing cylinder is expanded to a low pressure by an AXV expansion valve and then accepts heat from the freezing cylinder to cool the mix in the freezing cylinder. The refrigerant flowing to the hopper is expanded to a low pressure by a TXV expansion valve and then accepts heat from the hopper to cool the mix in the hopper. The refrigerant flowing to the hopper is between 22xc2x0 and 24xc2x0 F to keep the mix in the hopper between 37xc2x0 and 39xc2x0 F. After cooling the freezing cylinder and the hopper, the refrigerant is at a low pressure and high enthalpy and returns to the compressor for compression.
A liquid line solenoid valve is positioned at the inlet of each of the hopper and the freezing cylinder to control the flow of cool high pressure liquid refrigerant from the condenser to the hopper and the freezing cylinder. A hot gas solenoid valve is positioned at each of the inlet of the hopper and the freezing cylinder to control flow of hot gaseous refrigerant from the compressor discharge to the hopper and the freezing cylinder. When the system is in the cooling mode, the liquid line solenoid valves are opened and the hot gas solenoid valves are closed to allow the flow of high pressure liquid refrigerant to cool the mix in the hopper and the freezing cylinder. When the system is in the heating mode for nightly repasteurization, both the hot gas solenoid valves are opened and the liquid line solenoid valves are closed to allow the hot gaseous refrigerant to warm the mix in the hopper and the freezing cylinder.
When only the hopper is being cooled, not enough load is provided on the compressor, affecting compressor reliability. A hot gas bypass valve is opened to allow refrigerant gas from the compressor discharge to flow to the compressor suction to increase compressor load. Preferably, a solenoid valve is employed in series with the hot gas bypass valve to prevent leakage of refrigerant through the hot gas bypass valve.
An EPR valve is positioned proximate to the hopper discharge to maintain the evaporator pressure of the hopper, and therefore the temperature of the refrigerant flowing through the hopper. A CPR valve limits the inlet pressure of the compressor by reducing the amount of refrigerant flowing into the compressor suction. A solenoid valve proximate to the discharge of the freezing cylinder is closed when the freezing cylinder is not being cooled to prevent warm refrigerant from migrating around the freezing cylinder.
The system further includes a TREV valve to allow for liquid refrigerant injection to the compressor suction to control excessive compressor discharge during the cool cycle. When the compressor discharge temperature approaches 230xc2x0 F., the TREV valve is opened to allow the high pressure liquid refrigerant from the condenser to flow into the compressor suction, cooling the compressor suction and therefore the compressor discharge.
These and other features of the present invention will be best understood from the following specification and drawings.